Why is non-probability sampling used in quantitative research?

Non-probability sampling is often used because the procedures used to select units for inclusion in a sample are much easier, quicker and cheaper when compared with probability sampling. This is especially the case for convenience sampling.

Why is non-probability sampling bad?

The primary disadvantage of nonprobability sampling is the lack of generalizability. Samples that are more representative of a target population are more generalizable to the target population. Thus, the claims or findings of the study are more likely to also be found in the larger target population.